Offset breakwater configuration

ABSTRACT

Motion of a structure subject to the forces of impinging waves is substantially decreased and the transmission of wave motion past such structure accordingly diminished by providing the structure with a plurality of wave reflecting surfaces alternatingly offset from each other by a distance approximating one-half the wavelength of the impinging waves.

United States Patent [191 Moore OFFSET BREAKWATER CONFIGURATION [76] Inventor: Walter L. Moore, Taylor Hall 212-A, Austin, Tex. 78712 221 Filed: June 6, 1972 [21] Appl. No.: 260,274

[52] US. Cl. 61/5 [51] Int. Cl E02b 3/06 [58] Field of Search 61/5, 4, 6, 1

[56] References Cited UNITED STATES PATENTS 2,652,692 9/1953 Hayden 61/4 2,710,505 6/1955 Magill 61/4 2,994,201 8/1961 Hutchings 61/5 [111 3,800,543 [4 1 Apr. 2, 1974 12/1961 Wilson 61/4 12/1965 Miller et a1. 61/5 Primary Examiner-Mervin Stein Assistant Examiner-Philip C. Kannan [57] ABSTRACT Motion of a structure subject to the forces of imping' ing waves is substantially decreased and the transmission of wave motion past such structure accordingly diminished by providing the structure with a plurality of wave reflecting surfaces altematingly offset from each otherby a distance approximating one-half the wavelength of the impinging waves.

10 Claims, 19 Drawing Figures mm. 2 m4 SHEET 3 0F 4 FIG. 95

7 I A A A FIG. 95

FIG. 10

l OFFSET BREAKWATER CONFIGURATION SUMMARY OF THE INVENTION The present invention relates to the production of improved breakwaters. More specifically, the present invention is directed to breakwaters providing wave reflecting surfaces so disposed that when part of the wave is reflected at one surface, another part is reflected at a surface which is displaced by approximately one-half the wavelength of the incident wave. The displacement of the reflecting surfaces serves to balance and cancel out wave forces on the structure itself and can be adjusted to correspond to the desired or expected range of incident wavelengths. The breakwater may be floating and can be transportable and/or mobile.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the preferred embodiment of the present invention.

FIGS. 2 and 3 are sectional views 22 and 33 from FIG. 1.

FIG. 4 is a perspective view of an embodiment of the present invention wherein the offset reflecting surfaces are connected only by a skeletal framework.

FIG. 5 is a top view of a modification ofthe embodiment shown in FIG. 4 wherein the offset reflecting surfaces have the vertical edges thereof bent so as to project outward into the direction of an approaching wave front] FIGS. '6 and 7 are perspective illustrations of an embodiment of the invention wherein a single offset reflecting surface is placed between two floating barges. FIG. 6 is a view from above and in front of the structure. FIG. 7 is a view from underneath and behind the structure.

FIG. 8 is a top view of an embodiment of the invention having more than two offset planes of reflecting surfaces.

FIGS. 9A-9G are composites illustrating a number of possible alternative geometric shape embodiments encompassed within the present invention.

FIG. 10 is a plan view of a stable offshore work platform having the offset configuration built directly into one side thereof.

FIG. 11 is a representation of a group of river barges with the front barges offset in accordance with the present invention.

FIG. 12 is a representation of an embodiment of the invention similar to that illustrated in FIGS. 6 and 7 wherein the single offset reflecting surface is mounted in such a way as to move along tracks so that the offset distance between the reflecting surfaces may be varied in order to take into account changes in the wavelength of impinging waves.

FIG. 13 is a frontal view of'the embodiment illustrated in FIG.'12.

BACKGROUND OF THE INVENTION The basic objective of a breakwater is to reduce the height and energy of waves transmitted past it and thereby to protect that area which lies behind it, in relation to the wave front, from the effects of large amplitude wave action. Breakwaters provide an important and useful means for protecting beaches, harbors, loading docks, marinas, marine installations and the like.

Many proposed useful. amphibious operations make the development of transportable breakwaters desirable in order to provide safe, efficient and mobile landing and mooring conditions in areas where it is not convenient or economically practicable to provide a fixed breakwater. The floating structure may also serve as a pier or floating harbor or as a work platform for off shore activities such as well drilling. Additionally, floating breakwaters offer freedom from silting, scouring and foundation problems, as well as possible low initial cost for deep water applications.

Floating breakwaters may be said to have been designed primarily according to two basic theories. One

type of design serves to break up or attenuate the rotary circulation of water particles characteristic of waves. In effect, such breakwaters oppose the propagation of waves by acting todissipate the wave energy in small-scale water motions. The effectiveness of such breakwaters in opposing transmission of wave motion has, however, been only limited.

A second type of breakwater designinvolves the concept of reflecting waves back upon themselves. According to this concept a substantial portion of the wave energy'is ultimately dissipated in the reach of water from which the wave comes.

Breakwaters employing the reflecting type system have, however, also been only partially effective in preventing transmission of waves. Apparently because of the periodic wave forces acting on the structures them- DETAILED DESCRIPTION OF THE INVENTION The proposed floating breakwater of the instant invention is basically of the type of design wherein a surface is provided for reflecting the wave front back upon itself. Unlike previous designs, however, the present breakwater invention does not build up a wave transmitting motion within itself. I have discovered a design whereby the waveforces acting upon the breakwater structure itself can be counteracted and balanced internally. There is thus produced an essentially motionless structure which, of necessity, creates an area of still water in its lee.

The breakwater of the instant invention is illustrated in its preferred form in the drawings, FIG. 1. As shown in the drawing, the structure may be described as comprising a plurality of substantially rectangular wave reflecting surfaces R, each of which is offset from the next adjacent surface by a dimension which is approximately one-half the wavelength (L) of the waves expectedto be met by the breakwater. The effect of such an offset configuration is that a wave train approaching perpendicular to the reflecting surfaces of the breakwater will produce forces on the offset surfaces which are one-half cycle out of phase with each other. In other words, when the wave crest is at the first or frontal plane of reflecting surfaces, causing positive forces on the outer contact face, F,, as represented in FIG. 2, the wave trough is at the offset surfaces, causing negative forces on the inner contact face, F as represented in FIG. 3. Thus, the Wave generated forces on adjacent offset surfaces are at all times nearly equal and opposite to one another and motion of the breakwater structure is thereby substantially minimized.

The wave reflecting surfaces of the present invention are to be substantially vertical and may be constructed of any strong, rigid, self-supporting material, which may or may not be buoyant. Thus, it is contemplated that such materials as steel plate, sheet metal, molded fiberglass or some other resinous substance, wood and the like may be employed. Of course, if the material is not buoyant, suitable means for providing buoyancy must be provided (such as log means M in FIG. 1).

In the preferred embodiments of the present invention, it is contemplated that a flat lateral supporting surface, 0, be included perpendicular to and between each deflecting surface, the overall configuration of the breakwater thus taking on the form of the squaredof corrugated planar surface shown in FIG. 1. The addition of this lateral surface serves to maintain the slug of water in the approaching wave front in a coherent mass and to prevent any dispersing of the water around the edges of the reflecting surfaces.

However, it is also possible to utilize a structure comprised primarily of a number of surfaces in alternating offset planes connected only by some sort of a skeletal frame work. Such a structure is illustrated in FIG. 4. In such a construction, there should probably be a small amount of overlap of each back surface behind those in front in order to compensate for the slight dispersing of the slug of water as it passes by the front surfaces. Alternatively, this dispersion effect may be counteracted by constructing each of the wave reflecting surfaces with the edges projecting outward into the direction of the approaching wave front in a somewhat U- shaped cross section as shown in plan view in FIG. 5.

The number of separate reflecting surfaces in each of the offset planes is not critical and can be varied depending upon a number of circumstances. For example, the average expected wavelength, the depth of the body of water, the length of the desired breakwater, the size of the desired still water area, and of course structural and economic factors can influence the design. I have found for example that the concept of the present invention is adaptable to a single offset surface set between two floating barges each of which has a reflecting surface at one end as shown in FIG. 6. Similarly, breakwaters constructed according to the present invention may have the reflecting surfaces in more than two planes offset by multiples of one-half wavelength. Such a breakwater, a plan view of which is shown in FIG. 8, would be effective and may be preferred in a number of situations.

In all breakwater construction, it is contemplated that the lateral dimension, by which the offset planes of reflecting surfaces are separated and which ideally is to equal one-half a wavelength, be made adjustable in order to take into account the varied ranges of wavelengths which may be anticipated in any one circumstance. The offset distance between the reflecting surfaces may be set before installation of the breakwater in anticipation of an average expected wavelength, or

the breakwater may be constructed so that the distance may be adjusted as necessary. Such a construction would be of great utility in minimizing the amplitude of transmitted' waves during a wind storm for example, or some other occasion when the wavelength of the impinging waves differs from an expected value. One

manner in which this may be carried out is to construct the offset, lateral surface 0 in two separate parts, one

of which would be slidingly engaged with the other. Ali ternatively, either the forward or the rearward set of reflecting surfaces R may be mounted so they can move along guides or tracks placed parallel to the lateral surfaces 0. A releasable locking means, such as a brake, will maintain the reflecting surfaces in fixed relation. When the wave action changes, this brake may be released, allowing the waves themselves to adjust the length between the reflecting surfaces. This latter arrangement is illustrated in FIGS. 12 and 13 in connection with an embodiment of the invention similar to that shown in FIGS. 6 and 7. At the optimum offset distance, the brake may be reset again. Alternatively, the offset dimension may be made adjustable by any operable means, such as a built-in hydraulic screw or cable, a pneumatically controlled lever, or the like.

The necessity for adjusting the offset dimension as wavelengths vary may be lessened by designing the reflecting surfaces themselves for a range of wavelengths. A number of possible variations whereby this may be carried out, as well as some ideas for overcoming a slight change in wave direction, are shown in conceptual form in FIGS. 9A-9G. It is a remarkable aspect of the present invention that the efficiency of the offset configuration in preventing wave transmission remains essentially constant over a relatively broad range of wavelength variation even without such modifications.

In general, the breakwater should be constructed so that the top of the reflecting surfaces remains above the height of the impinging waves. As far as the. draught, or penetration beneath the still water level, the critical criterion is that the surfaces must intercept most of the water motion. As is well known, in deep water, water motion will be a function of wavelength, whereas in relatively shallow areas it will be a function of the water depth. Any design whereby a substantial portion of the water motion is intercepted will be acceptable.

In order to improve the effectiveness of breakwaters which are subject to waves having significantly large wavelengths it may be desirable to have the vertical surfaces extend deeper into the water by such means as placing an addition (or skirt) along the length of each surface. In this manner the tendency of the waves to break apart and disperse, thus possibly contributing to a pitching motion of the structure, would be cut down considerably. Such a skirt is shown at k in FIG. 6.

Similarly, it may be desirable to attach a lip or flange along the bottom edge of the offset reflecting surfaces and/or the longitudinal surfaces 0. The flange may be added to either the barge configuration as shown in FIGS. 6 and 7 or to the basic configuration as shown in FIG. 1. Such a lip or flange will cause flow separation and reduce the flow of water under the breakwater surfaces, thus reducing any vertical heaving or pitching motion caused by periodic flow under the breakwater acting on the bouyancy elements. Further, the heaving and pitching motion may be reduced due to the drag of such flanges resisting motion through the water.

In no way intending to limit the scope of the present invention, but rather by way of giving a fuller, more complete description thereof, a number of potential applications of the floating breakwater of the present invention are indicated below:

1. To create a body of relatively still water so as to protect-a marina or boat harbor fromthe wave action of a larger body of water such as a lake or a bay.

2. To provide a stable platform for offshore work such as oil well drilling in locations subject to wave action. The offset wave deflecting configuration could be built directly into the side of such a platform as illustrated in FIG. 10, or when the expected wavelength is very large, two or more platforms could be connected together with a planar surface which would serve as the offset plane'while the ends of the platform would serve as the frontal reflecting plane. The latter concept is that illustrated in FIG. 6.

3. To serve as a skimmer to confine lower density liquid to a particular area of a body of water. For example, it is well known that heated water has a lesser density than cold water. In a body of water subject to the influx of a significant quantity of heated water, for example the discharge from a power plant, a floating breakwater would confine the heated water to a portion of the body of water. As the heated water cools, or is displaced by the inflow, it will flow under the skimmer and into the main portion of the body of water. In this way the thermal pollution can be confined to a smallportion of the body of water relieving the temperature effecton the remainder. This concept may also be employed as a means for collecting and containing oil slicks or other surface-floating contaminants. A skimmer constructed according to the present invention would not only act to contain and confine lower density liquids but would act to retard mixing due to wave motion.

4. To provide wave protection for offshore ports or terminal facilities for super-size tankers on coast lines where the water depth is insufficient in natural harbors. Floating breakwaters constructed in accordance with the present invention could be made self-propelled or could be anchored in a pattern to protect terminal facilities and super tankers during loading or unloading operations. An additional advantage of such breakwaters would be to contain any lighter-than-water substances which might be accidentally spilled during use of the terminal facilities.

5. Theoffset configuration concept of the present invention may be utilized to render the power requirements in transporting groups of barges on inland waterways. On these waterways such things as freight, garbage, and the like are loaded on barges, a number of which are then tied together'and pushed along the body of water by-one or more tug boats. The action of the frontal surface of the group of barges being pushed along the water creates a wave front. Ifa numberof the front barges were arranged in offset configuration, at one-half of the wavelength of the created wave in accordance with the present invention, this would serve to cut back on the drag experienced and thereby decrease the amount of power necessary to move the said wave reflecting surfaces being arranged in at least two sets of one or more surfaces,

each of the said sets being spatially located in substantially a single vertical plane;

each said vertical plane being separated by a distance measured in the direction of approach of impinging waves, approximately equal to one-half the wavelength of the waves expected to impinge upon said surfaces;

the surfaces in eachsaid vertical plane being separated from one another and arranged in such fashion that each surface lies directly behind a gap between the surfaces of the plane in front thereof;

the sum of the surface area of all the surfaces in any one plane being approximately equal to the total surface area in each of the other planes;

the number and arrangement of all reflecting surfaces being such that the net moment about the center of the structure span approximates zero.

2. A structure as in claim 1 wherein means are provided for varying the distance by which the planes of reflecting surfaces are separated in order to take into account changes in the wavelength of impinging waves.

4. A structure as in claim 3 wherein means are provided for permitting variation of the offset distance between adjacent wave reflecting surfaces.

5. The structure of claim 4 wherein a releasable locking means is provided for maintaining the offset distance fixed yet permitting adjustment when necessary.

6. The structure of claim 1 formed by setting a single offset reflecting surface between two floating barges each having a reflecting surface in approximately the same vertical plane and substantially parallel to said offset reflecting surface.

7. The structure of claim 6 wherein the surfaces thereof are extended farther below the still water level by the addition of a rigid skirt along the length of the bottom of each surface.

8. The structure of claim 7 wherein said rigid skirt has a flange along the bottom edge thereof.

9. The method of internally balancing and thereby substantially diminishing periodic motion generating forces in a floating structure which is subject to the action of impinging waves which method comprises:

forming a series of substantially vertical wave reflecting surfaces adjacent to that part of the floating structure which faces the approaching wave fronts;

situating said reflecting surfaces in at least two vertical planes located one behind each other perpendicular to the direction of the approaching wave front and maintaining the distance said planes are separated at a value approximately equal to onehalf the wavelength of the impinging waves; said reflecting surfaces being arranged in said vertical planes in alternating, offset fashion in such manner that the total surface area in each plane is approximately equal and the net moment about the center of the total span of the wave reflecting surfaces approximates zero. 10. The method of claim 9 wherein one or more of the wave reflecting surfaces are provided by the floating structure itself.

22;;3? 4 v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,800,543 Dated April 11, 197

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, lines 11-14, reading "This latter arrangement is illustrated in FIGS. 12 and 13 in connection with an embodiment of the invention similar to that shown in FIGS. 6 and 7." should be inserted in Column 4, line 7,

after the "O.

Column 5, line 46, "render" should read reduce--.

Signed and sealed this 24th day of September 1974.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents McCOY M. GIBSON JR. Attesting Officer 

1. A mobile, buoyant structure comprising a plurality of substantially vertical, substantially rectangular wave reflecting surfaces; means for supporting said wave reflecting surfaces in a substantially vertical position so that waves impinging thereon will be reflected back upon themselves; said wave reflecting surfaces being arranged in at least two sets of one or more surfaces, each of the said sets being spatially located in substantially a single vertical plane; each said vertical plane being separated by a distance measured in the direction of approach of impinging waves, approximately equal to one-half the wavelength of the waves expected to impinge upon said surfaces; the surfaces in each said vertical plane being separated from one another and arranged in such fashion that each surface lies directly behind a gap between the surfaces of the plane in front thereof; the sum of the surface area of all the surfaces in any one plane being approximately equal to the total surface area in each of the other planes; the number and arrangement of all reflecting surfaces being such that the net moment about the center of the structure span approximates zero.
 2. A structure as in claim 1 wherein means are provided for varying the distance by which the planes of reflecting surfaces are separated in order to take into account changes in the wavelength of impinging waves.
 3. A structure as in claim 1 wherein the wave reflecting surfaces are arranged in alternating, offset fashion in two vertical planes and are joined to one another by rigid, lateral surfaces perpendicular to said wave reflecting surfaces, such that the overall configuration of the structure takes on a squared-off corrugated form.
 4. A structure as in claim 3 wherein means are provided for permitting variation of the offset distance between adjacent wave reflecting surfaces.
 5. The structure of claim 4 wherein a releasable locking means is provided for maintaining the offset distance fixed yet permitting adjustment when necessary.
 6. The structure of claim 1 formed by setting a single offset reflecting surface between two floating barges each having a reflecting surface in approximately the same vertical plane and substantially parallel to said offset reflecting surface.
 7. The structure of claim 6 wherein the surfaces thereof are extended farther below the still water level by the addition of a rigid skirt along the length of the bottom of each surface.
 8. The structure of claim 7 wherein said rigid skirt has a flange along the Bottom edge thereof.
 9. The method of internally balancing and thereby substantially diminishing periodic motion generating forces in a floating structure which is subject to the action of impinging waves which method comprises: forming a series of substantially vertical wave reflecting surfaces adjacent to that part of the floating structure which faces the approaching wave fronts; situating said reflecting surfaces in at least two vertical planes located one behind each other perpendicular to the direction of the approaching wave front and maintaining the distance said planes are separated at a value approximately equal to one-half the wavelength of the impinging waves; said reflecting surfaces being arranged in said vertical planes in alternating, offset fashion in such manner that the total surface area in each plane is approximately equal and the net moment about the center of the total span of the wave reflecting surfaces approximates zero.
 10. The method of claim 9 wherein one or more of the wave reflecting surfaces are provided by the floating structure itself. 